Welded steel structure



Dec. 21, 1943. J. o. JACKSON WELDED STEEL STRUCTURE Filed Jan. 6, 1942A//oy cons/:fing o/zZya fro/z carbon and m'cke ca/"a/z ma I NVE NTORPatented Dec. 21, 1 943 2,337,049 WELDED STEEL STRUCTURE James 0.Jackson, Crafton,

Pa., assixnor to Pittll hurgh-Des Moines Company, a corporation ofPennsylvania Application January 8, 1942, Serial No. 425,758 z claims.(ci. 22o-1) This invention relates to steel structures i'or use at lowtemperatures, some or all of the component parts of which are united bya welding operation.

It is well-known that ordinary welded steel structures are notsatisfactory for use at low temperatures. Both the steel and the weldsbecome embrittled to such an extent that the structures fail whensubjected to load. 'I'hese failures manifest themselves by cracking andrupturing of the steel or welds and are directly related to loss -ofductility at the low temperatures involved.

It is generally accepted by engineers that a structural steel or partmust have a Charpy impact value of at least ft. lbs. before it can beused in engineering structures. Below that value the ductility isunsatisfactory. The usual grade of structure steel suitable for theproduction of electrically welded products has at ordinary temperaturesan average Charpy impact value rangs ing from about 60 ft. lbs. at 100F. to about 43 ft. lbs. at 0 F. Below 0 F. the impact value is erraticand tests show that at -50 F. Charpy impact values are obtained whichvary within the rather broad range of 6-38 ft. lbs. At 100 F. ordinarystructural steel has a Charpy impact valueof about 2-3 ft. lbs. Thissignifies practically complete loss of ductility and such material is,therefore, unsuited for use in steel structures which are subjected toload. By usual or ordinary structural steel, I mean a steel which has acarbon content up to approximately 0.35% with the balance iron exceptfor the usual contaminants in normal amounts.

It is also known that some materials are satisfactory for use in lowtemperature work in constructing load-bearng structures but that theseare unduly expensive. Therefore, for large structures the cost becomesprohibitive and frequently also the use of such materials gives rise toother problems, particularly welding problems. The austenitic stainlesssteels containing about 18% chromium, about 8% nickel, with low carbonand the balance iron except for the usual contaminants in normal amountsare theoretically satisfactory for low temperature work but,practically, are not employed because of the inordinate expense and thedifiiculty in welding such material. Copper and aluminum are alsocapable of being employed at low temperatures without undue loss ofductility but they too are expensive and at the present time scarce.Even where it has been possible to employ metals or alloys which areimpact value of at themselves capable of retaining adequate ductility atlow temperatures, it has not been possible to weld the same in suchmanner that the welds resist embrittlement at such temperatures.Therefore, engineers are still seeking a moderately priced materialwhich can be employed at low temperatures and which can be welded insuch manner that the welds are at least as substantially resistant toembrittlement as the base metals or alloys themselves. So far as I amaware, this problem has not heretofore been successfully solved and itis with the solution of this problem that my present invention isconcerned.

One of the objects of my present invention, accordingly, is to producewelded structures in which both the base material and the welds areresistant to embrittlement even at temperatures as low as 260 F. andwhich at such temperatures have a Charpy impact value af 10 ft. lbs. ormore.

Another object of my invention resides in producing welded structureswhich have a Charpy least 10 ft. lbs. at temperatures as low as 260 F.and in which the composition of the base metal or alloy and thecomposition of the weld metal are predeterminedly correlated.

A futher object of my invention resides in producing welded structurescomposed of component parts of nickel-modified steel and weld metal ofspecial composition and in which the minimum impact value ture ranges-280 F.

Other and further objects and advantages will either be pointed out inthe following description or will bev understood or appreciated by thoseversed in this subject.

The attached drawing forming part of this application illustrates aWelded steel structure embodying this invention. l

In the drawing:

Figure 1 is a sectional view of the inner shell of a welded steelstorage tank embodying this invention and in this view, the width of theweld bands is exaggerated for the purpose of illustration.

of any portion of the welded strucfrom about 18-20 ft. lbs. at aboutFig. 2 is a fragmentary sectional view taken through a typical weld seamuniting adjacent parts of the structure of Fig. 1.

In carrying out my present invention I preferably employ as a basematerial, i. e.. the material of the plates or other component parts ormembers which are to be welded into a desired struc- A nickel content oiapproximately 31/2% is pre- 'ierred but I have found that nickel may besatisfactorily employed within the range ci about 0.510%. v

This steel is cast in ingot molds in the conventional manner and ispreferably deoxidized by the addition thereto of approximately .08%aluminum while the steel is still in the molten state. The ingots 'arereduced in the usual'manner and rolled into plates, bars and otherdesired shapes, hereinafter designated as compo nent structural parts.After rolling, the component structural parts should preferably benormalized at a temperature oi about i550o F.

After the fabrication of the component structural parts, they may beproperly prepared for welding in known manner, as by" cleaning, picklingSandblasting, polishing, or the like. I then preheat the componentstructural parts to a temperature ranging from about l70-350 F. 'Whilethe entire parts can, if desired, be raised to preheating temperature, Ihave found that it is only essential that those areas of the parts bepreheated which are adjacent the metal which is to be welded. Thewelding operation is carried out by means of the known electric arc process, using a covered metallic electrode which contains about itl-30% ofchromium with the balance iron except for a percentage of nickel whichmay range from about l-30%. By employing covered electrodes, atmosphericgases are excluded and better welds are thus secured. The use of coveredelectrodes is known in welding and is not per se deemed to be a part ofthe present invention. Uncovered electrodes may be employed with successbut the best results are secured by using covered electrodes. Inconnecgs tion with the composition oi the electrode, I have discoveredthat a metallic electrode containing approximately 25% chromium andapproximately 20% nickel with timum results, and this particularelectrode composition is, therefore, deemed to be an important part oimy present invention.

Welds made in accordance with the foregoing procedure are characterizedby the fact that the base metal or material is not penetrated by ltheweld metal to a very great or deep extent. There is a definite alloyingof the weld metal and the base metal or material such as ischaracterized, for example, by parts united by brazing. In practicingthe present invention, I have been able to secure butt-welded joints inplates of the base material above speciiied having a Charpy impact valueof aboutl 18-20 ft. lbs. at a temperature oi 260 F. The welded structureso produced is further characterized by the fact that such values areequaled or exceeded in the weld metal itself and in the fusion andheat-aected zones adjacent the welds. So far as I know,

2 ture. a steel having the following composition: tusse remite areunique and have not heretofore Percent been even approximated. A

Col-boul About o m to 0 3@ `Welded structures as above described andpro. Manganese About 0 30 to 0 5o duced in accordance with the procedureset forth Silicon About, 0 10 to 03o 5 are especially adapted for use inlow temperature Nickel About 3 0 to 4 0 containers. 1- c" thcse forstoring liqueiied natural sulphur Up to about 0,04 8&5 and Othermaterials as typiiled by my eo- Phosphorg Up to abgut 0.04 applicatmnsSerial N0., 426,012, led non Balance January s, 1942, and serial No.426,192. nieu January 9, 1942. It is to be particularly noted,furthermore, that I employ welding compositions having or more oi'ironwhile still obtaining welds that are fully satisfactory at lowtemperatures, even temperatures down to about 260 F. or less. This hasboth economic and structural advantages as will be appreciated.

in important feature or my new procedure resides in the preheating stepin which connection areas of the component structural parts adjacent themetal to be united by the welding operation are raised to a temperature.above the prevailing ambient temperature but not to a temperature highenough to bring about adverse changes in respect to ductility or grainsize.

'. It is to be further understood that the Precent invention may beemployed in connection with the use of a backing-up strip for the weldmetal as illustrated in my aforesaid copending application, Serial No.a26,0l2.

The foregoing is to be understood as illustrative and not as restrictiveand within the purview hereof I may resort to other and furtheradditions, omissions. substitutions and modications without departingfrom the invention, the scope of which is rather that deiined by theappended claims.

Having thus described my invention, -what l claiins as new and desiretosecure by Letters Paten l.. A weldedsteel structure which duringnormal use is subjected to load while at a temperature below 100 F.,which is characterized by the remainder iron gives oppossessing aminimum Charpy impact value o1 at least 10 foot pounds at a temperatureas low as about 260 F. and which is fabricated from component structuralparts formed from alloy steel consisting only of iron, carbon andnickel, except for usual impurities in common amounts, the carboncontent ranging from about 0.10% to 0.30%, and the nickel contentrangingfrom 3.00% to not over 10.00%; said parts being united by weld metalconsisting only of iron, chromium and nickel, except for usualimpurities in common amounts; the chromium content of said weld metal@ranging from about 20.00% to not over 30.00%, the nickel content rangingfrom about 18.00% to about 25.00% and the carbon content not exceeding0.30%.

2. A tank for storing liquefied gas at a temperature in the neighborhoodof 260 F. and which at such temperature has a ductility represented by aCharpy impact value of at least l0 root pounds, said tank beingfabricated from a plurality of butt welded alloy steel plates of thecomposition set forth in claim l and in which the weld metal unitingsaid plates is deposited weld metal and has the same composition as theweld metal set forth in claim l.

JAMES O. JACKSON.

